1. Field of the Invention
The instant disclosure relates to a light emitting diode (LED); in particular, to a signal generating method and a circuit for controlling dimming of the LED.
2. Description of Related Art
A conventional method for controlling dimming of an LED is generating a pulse width modulation (PWM) signal for switching the transistor connected to the LED. A conventional pulse width modulation signal is shown in FIG. 1A. The duty ratio D shown in FIG. 1 is determined by control bits. Based on cost down considerations, the frequency of the pulse width modulation signal is not high, such that the length T of the pulse width modulation signal is longer when more control bits are used. For a case of LED display controlled by control bits of 16-bits, the minimum pulse-width of the pulse width modulation signal is N (N is an integer), the duty ratio can be changed by an interval of the length of 1/N. Thus, the pulse width modulation signal can correspond to 65536 gray levels by changing the duty ratio D from minimum duty ratio (which is zero) to the maximum Dmax (which is the length T), as shown in FIG. 1B. Accordingly, the length T of the pulse width modulation signal would certainly be long, and it will take more time to display a frame. As a result, the frame rate (or frame frequency) would be quite low.